1. Field
Systems and methods herein relate generally to monocrystalline germanium ingots/wafers and in particular to growth of such ingots/wafers with reduced micro-pit density (MPD).
2. Description of Related Information
Electronic and opto-electronic device manufacturers routinely require commercially grown, large and uniform single semiconductor crystals which, when sliced and polished, provide substrates for microelectronic device production. The growth of a semiconductor crystal involves heating raw material to its melting point to create a crystalline raw material melt, bringing the melt into contact with a high quality seed crystal, and allowing the crystallization of the melt when in contact with the seed crystal. A number of different processes for accomplishing this are known. These include the Czochralski (Cz) process and its variant the Liquid Encapsulated Czochralski (LEC) process, the Horizontal Bridgman and Bridgman-Stockbarger processes (HB) and their vertical variants (VB), and the gradient freeze (GF) and its variant, the vertical gradient freeze (VGF) processes. See for example “Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials” P. Clapper, Ed., John Wiley and Sons Ltd, Chichester, England, 2005, for general discussions of these techniques and their application to the growth of various materials.
The crystallization of the melt forms an essentially cylindrical crystal (an ingot) along a vertical axis with the seed crystal below the crystalline raw material(s). The equipment necessary to form the semiconductor crystal includes a crystal growth furnace, an ampoule, a crucible, and sometimes a crucible support. The crucible may also have a lower, narrow portion, called a seed well.
Drawbacks exist with the conventional crystal growth process and crystal growth equipment. For example, known crystal growth processes often create crystals that have excessive micro-pits or micro-cavities which result in imperfections, flawed devices and/or otherwise reduce the overall useful quantity of the crystal grown using such processes. Such issues and reduction in useful grown crystal quantity result in a lower yield. Accordingly, there is a need for a crystal growth systems and methods that reproducibly provide high quality ingots/wafers and otherwise overcome such drawbacks in existing systems.